Precise definition of the term, ‘native speaker’, is extremely difficult and therefore usually avoided even though the concept is vital in SLA as in many other domains dealing with language ability. Most researchers rely on the assumption that there is a common understanding of what a native-speaker is. However, the requirements of scientific rigour make a close examination of this ‘common understanding’ an absolute necessity. We argue that reformulating the concept along the lines first suggested by Eleanor Rosch, i.e. using prototype theory, should provide the best way of introducing the necessary precision. This has the consequence that native-speakerhood becomes a gradient term with, respectively, core (prototypical) and peripheral features. This allows researchers to be more precise about what they, or the particular theoretical approach they adopt, claim to be the essential and non-essential features of nativeness and the necessary rigour is thereby achieved.